Sound-absorbing structure and sound-absorbing unit

ABSTRACT

Sound-absorbing unit is provided with a high sound-absorbing/insulating capability. The sound-absorbing unit ( 60 ) includes a corrugated partition plate ( 52 ) whose antinode portions ( 52   a   , 52   b ) extend in a first direction (Y); a sound-absorbing material ( 51 ) provided on the corrugated partition plate ( 52 ); and a second partition plate ( 53 ) which extends in a second direction (X) and which partitions air portions ( 70 ) defined between the corrugated partition plate ( 52 ) and the sound-absorbing material ( 51 ).

TECHNICAL FIELD

The present invention relates to sound-absorbing structure andsound-absorbing unit that absorb a grating noise. More specifically, thepresent invention relates to sound-absorbing structure andsound-absorbing unit with partition plates that divide the air layerbehind a sound-absorbing material.

BACKGROUND ART

Sound-absorbing unit with partition plates, which divide the air layerbetween a sound-absorbing material and a base plate into a plurality oflattice ‘cells’, is known, as disclosed in JP,11-161282,A. In thissound-absorbing unit, the height of the air layer in the sound waveincident direction is set to one-fourth of the wavelength of a targetsound. This enables the energy of the sound wave to be absorbedefficiently. Thus, according to the conventional sound-absorbing unit, asound absorbing coefficient for a particular frequency component isimproved, and it becomes possible to reduce the weight of thesound-absorbing unit while maintaining its high sound absorbingcoefficient.

Generally, sound-absorbing unit is positioned such that it surrounds thesound source. In the space where the sound-absorbing unit is placed,there are a variety of sound waves. For example, there are sound wavesincident indirectly into sound-absorbing unit via reflections at thestructures around the sound source as well as the ones incident directlyinto sound-absorbing unit from the sound source. Thus, the variety ofincident directions becomes wide. Especially in a closed space such asthe engine room of a vehicle and a cabin, etc., the variety of thetraveling directions of sound waves is quite wide because thereflections of the sound waves occur repeatedly. For this reason, inorder to improve its overall sound-absorbing performance,sound-absorbing unit is required to achieve a good sound-absorbingperformance for the sound waves with a variety of incident directions.

Further, sound-absorbing unit is required to have a structure orperformance suitable for its installation place. For example, in thecase of being installed in a cabin, the sound-absorbing unit should havea sound-absorbing configuration on its inner side suitable for absorbingthe grating noise in the cabin, while it should have a sound-insulatingconfiguration on its outer side suitable for insulating the noisetransmitted into the cabin from outside. Furthermore, if sound-absorbingunit additionally serves as an interior component, it is required tohave sufficient strength and durability as an interior component.

In particular, the above-mentioned conventional sound-absorbing unit hasdefects in terms of sound-insulating characteristics. In such cell-typesound-absorbing unit, sound waves are likely to be transmitted into thecabin from outside because the partition plates that define cells don'thave a function of blocking the sound waves passing through the cells.

DISCLOSURE OF INVENTION

It is a general object of the present invention to providesound-absorbing structure and sound-absorbing unit that have a highsound-absorbing capability as well as a high sound-insulating capabilityand that can provide an efficient sound-absorbing effect centered on aparticular target frequency.

In order to achieve the above-mentioned objects, according to one aspectof the present invention a sound-absorbing structure, comprising: asubstantially flat support base; a substantially flat sound-absorbingmaterial arranged substantially parallel to the support base; and acorrugated partition plate interposed between the support base and thesound-absorbing material, the corrugated partition plate having upperantinode portions opposed to the sound-absorbing material and lowerantinode portions opposed to the support base; wherein the lowerantinode portions of the corrugated partition plate are at leastpartially separated from the support base.

In the above-mentioned aspect of the present invention, between thesound-absorbing material and the support base is provided the corrugatedpartition plate. Thus, the sound waves coming from the support base'sside lose a large amount of energy thereof when they pass through thecorrugated partition plate. Further, there is a gap (separation) betweenthe lower antinode portions of the corrugated partition plate and thesupport base. Thus, the vibration of the support base cannot betransmitted to the corrugated partition plate directly. This improvesthe sound-insulating effect of the sound-absorbing structure withoutinterposing a conventional acoustic insulating material withhigh-destiny/thickness/weight between the corrugated partition plate andthe support base.

Additionally, the lower antinode portions of the corrugated partitionplate may be supported via an elastic element. This effectively lessensthe transmission of the vibration of the support base to the corrugatedpartition plate. Additionally, the lower antinode portions of thecorrugated partition plate may be supported by low-vibration portions ofthe support base, such as reinforced portions with strengthening ribsand the like. This also lessens the transmission of the vibration fromthe support base to the corrugated partition plate. As a result, itbecomes possible to improve the sound-insulating effect of thesound-absorbing structure without interposing a conventional acousticinsulating material with high-destiny/thickness/weight between thecorrugated partition plate and the support base.

According to another aspect of the present invention a sound-absorbingunit comprising: a corrugated partition plate having a first side and asecond side opposite to the first side; a substantially flatsound-absorbing material provided on the first side of the corrugatedpartition plate; and at least one second partition plate configured topartition air spaces defined between the sound-absorbing material andthe corrugated partition plate.

In the above-mentioned aspect, the second partition plate partitions theair spaces that extend in a first direction, in which antinode portionsof the corrugated partition plate extend, between the corrugatedpartition plate and the sound-absorbing material. By virtue of thesecond partition plate, the entry of the sound waves in a slantingdirection at an angle to the first direction can be limited, whichenables the concentration of the sound-absorbing effect on a desiredfrequency band. As a result, it becomes possible to keep the overallsound-absorbing effect high even if the sound-absorbing unit is placedin such a sound field where the sound waves may enter into thesound-absorbing unit from various directions. Furthermore, by virtue ofthe second partition plate, the in-plane rigidity of the corrugatedpartition plate increases and thus the potential for deformation of thecorrugated partition plate decreases. Thus, it becomes possible to givethe sound-absorbing unit the required strength as an interior component.

Additionally, the second partition plate may extend in a directionsubstantially perpendicular to the first direction in which antinodeportions of the corrugated partition plate extend.

Additionally, sound-absorbing materials may be provided respectively onboth sides of the corrugated partition plate. With this arrangement, itbecomes possible to absorb the sound waves incoming from variousdirections on both sides of the sound-absorbing unit and to furtherimprove the overall sound-absorbing effect of the sound-absorbing unit.

Additionally, the second partition plate may be configured to partitionthe air portions only on the first side of the corrugated partitionplate. With this arrangement, miniaturization of the second partitionplate and weight reduction are enabled while maintaining theabove-mentioned high sound-absorbing effect on one side.

Additionally, the corrugated partition plate may include a wave patternwhose phase and/or amplitude is varied at a boundary between thecorrugated partition plate and the second partition plate. Thisarrangement allows the sound-absorbing unit to deliver thesound-absorbing performance over a wide frequency band and increases anout-plane rigidity and thus durability of the second partition plate.

Additionally, the corrugated partition plate may include a sine wavepattern and/or a rectangular wave pattern. The corrugated partitionplate with a sine wave pattern among others has high stiffness and thusleads to improvement in the sound-insulating effect. Furthermore, withthe corrugated partition plate with sine wave pattern among others, theentry of the sound waves into the air spaces can be promoted effectivelysince the acoustic impedance changes gradually.

Additionally, the corrugated partition plate may include wave patternswith different frequencies and/or different amplitudes. With thisarrangement, it becomes possible to gain a sound-absorbing effect over awide frequency band and optimize the sound-absorbing effect according tothe characteristics of the sound field in the vicinity of thesound-absorbing unit.

According to another aspect of the present invention a sound-absorbingunit is provided that includes a partition plate having recesses; and asound-absorbing material which covers air portions defined inside therecesses.

In the above-mentioned aspect of the present invention, the partitionplate having recesses can be formed from a sheet material. This leads toa reduction in parts count for the sound-absorbing unit and increasesproductivity for manufacturing the sound-absorbing unit whilemaintaining the above-mentioned high sound-absorbing/insulating effect.Further, this arrangement can limit the entry angle of the sound wavesin a slanting direction with respect to the sound-absorbing unit. As aresult, the sound waves incident from various directions can be absorbedefficiently and the sound absorbing effect is not distributed over awide frequency range other than the target frequency range.

Additionally, each recess may have a cross-sectional area that graduallyvaries with the depth of the recess. A partition plate with suchrecesses has a high stiffness against loads applied from variousdirections. This arrangement leads to improvement in thesound-insulating effect of the partition plate as well as in thedurability of the sound-absorbing unit. Furthermore, since the acousticimpedance changes gradually inside the recesses, the entry of the soundwaves into the recesses can be promoted effectively.

In the above-mentioned aspects of the present invention, the thicknessof air portions behind the sound-absorbing material may be set to oddmultiples of one-fourth of the wavelength of sound waves of targetfrequencies. With this arrangement, the sound waves input in airportions can be absorbed efficiently, because the sound waves passthrough the sound-absorbing material at maximum particle velocity.

Other objects, features and advantages of the present invention willbecome more apparent from the following detailed description when readin conjunction with the accompanying drawings.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1A is a conceptual rendering for illustrating a state of soundwaves incoming in a perpendicular direction with respect to thesound-absorbing unit.

FIG. 1B is a conceptual rendering for illustrating a state of soundwaves incoming in a slanting direction with respect to thesound-absorbing unit.

FIG. 1C is a conceptual rendering for illustrating a state of soundwaves in the case of the sound-absorbing unit with partition plates.

FIG. 2A is a diagram for showing a sound-absorbing effect centered on aparticular frequency.

FIG. 2B is a diagram for showing a sound-absorbing effect spreading overa wide frequency band depending on the cell width W.

FIG. 3A is a cross-sectional view of a sound-absorbing unit according tothe first embodiment of the present invention.

FIG. 3B is a perspective view of the partition plate of thesound-absorbing unit of the first embodiment.

FIGS. 4A-4C are diagrams for showing variations in placing the partitionplate of the sound-absorbing unit.

FIGS. 5A-5D are diagrams for showing alternative embodiments of thepresent invention.

FIG. 6A is a cross-sectional view of a sound-absorbing unit according tothe second embodiment of the present invention.

FIG. 6B is a perspective view of the partition plates of thesound-absorbing unit of the second embodiment.

FIG. 7 is a cross-sectional view for showing a variant of thesound-absorbing unit according to the present invention.

FIGS. 8A and 8B are cross-sectional views of the sound-absorbing unitfor showing alternative embodiments of the present invention.

FIG. 9A is a perspective view of a sound-absorbing unit according to analternative embodiment.

FIG. 9B is a cross-sectional view of the sound-absorbing unit of FIG.9A.

FIGS. 10A-10C are diagrams for showing variations of a wave pattern ofthe corrugated partition plate.

FIG. 11A is a cross-sectional view of a sound-absorbing unit accordingto the third embodiment of the present invention.

FIG. 11B is a perspective view of the partition plate of thesound-absorbing unit of the third embodiment.

FIG. 12A is a cross-sectional view of the partition plate according toan alternative embodiment taken on the line A-A or B-B of FIG. 12B.

FIG. 12B is a perspective view of the sound-absorbing unit of thealternative embodiment of FIG. 12A.

BEST MODE FOR CARRYING OUT THE INVENITON

Hereafter, the preferred embodiments according to the present inventionare explained with reference to the drawings.

First, a fundamental principle on which the present invention is basedis described prior to the description of sound-absorbing unit accordingto the present invention. FIGS. 1A-1C are conceptual renderings forillustrating a state of sound waves incident on a sound-absorbingmaterial 30 from above, with an air layer 32 being between a supportbase 34 and the sound-absorbing material 30.

Referring to FIG. 1A, if the sound waves with wavelength λ enterperpendicularly with respect to the support base 34, standing-waves areformed by a combination of incident waves and reflected waves. Thestanding-waves have antinodes at the points that are separated from thesupport base 34 by distances of odd multiples of one-fourth of thewavelength λ. The particle velocity of sound waves becomes its maximumat the antinodes. Thus, if the sound-absorbing material 30 is located atthe point where the particle velocity of sound waves becomes a maximum,the sound-absorbing efficiency will be maximized because the sound wavespass through the sound-absorbing material 30 at their highest energylevel. In other words, setting the thickness of the air layer 32 betweenthe support base 34 and the sound-absorbing material 30 to odd multiplesof one-fourth of the wavelength λ of the target sound waves to beabsorbed can significantly increase the sound absorbing coefficientaround the frequency of the target sound waves.

On the other hand, if the sound waves enter in a slanting direction, asshown in FIG. 1B, the above-mentioned standing-waves aren't formed.Thus, in a sound field in which there are a variety of incidentdirections of sound waves, such as in a sound field inside the cabin ofa vehicle, the sound absorbing effect will be distributed over a widefrequency range other than the target frequency range, resulting in adecrease in the overall sound absorbing capability. In addition, sincethe sound absorbing effect is distributed over wide frequency range andthe sound pressure level is reduced universally over the wide frequencyrange, the sensory effect as perceived by a human cannot be improved.

One approach to solve this problem is to divide the air layer 32 into aplurality of cells by placing partition plates 36 that limit theincidence of sound waves in slanting directions, as shown in FIG. 1C. Inthis case, the above-mentioned standing-waves are formed even in a soundfield with sound waves of a variety of incident directions. The distanceW1 defines the range of incident angles of sound waves that can enterinto cells. Thus, by determining the distance W1 as desired, forexample, it becomes possible to concentrate the sound-absorbing effectinto the area around the target frequency, as shown in FIG. 2A, or todistribute the sound-absorbing effect over the desired frequency bandcentering on the target frequency, as shown in FIG. 2B.

According to the one aspect of the present invention describedhereafter, a sound-absorbing unit is provided that is equipped with asound-absorbing/insulating structure with increasedsound-absorbing/insulating capability based on the above-mentionedprinciple.

FIG. 3A is a cross-sectional view of a sound-absorbing unit according tothe first embodiment of the present invention. FIG. 3B is a perspectiveview of the partition plate of the sound-absorbing unit of thisembodiment. The sound-absorbing unit 50 consists of a sound-absorbingmaterial 51 and a partition plate 52.

The partition plate 52 according to the first embodiment has awave-shaped cross-section with the upper and lower antinode portions 52a, 52 b, respectively, extending substantially in parallel with eachother in a constant direction. Although the corrugated partition plate52 is made of stamped aluminum plate in terms of weight reduction, itcan be made of hard resin such as polypropylene-based resin or steel,etc.

The pitch W1 between the neighboring upper antinode portions 52 a may bedetermined, based on the above-mentioned principle, considering thetarget frequency band and the characteristics of the sound field aroundthe sound-absorbing unit 50. It is noted that each of the antinodeportions 52 a, 52 b of the corrugated partition plate 52 don'tnecessarily extend in parallel spaced at regular intervals, and don'tnecessarily extend linearly. For example, the antinode portions 52 a, 52b may be curved. Accordingly, the pitches W1 may be set differentlybetween every two neighboring antinode portions 52 a, 52 b, and/or thepitch W1 may be varied along the direction of the antinode portions 52a, 52 b.

The sound-absorbing material 51 is made of processed metal fiber such asaluminum fiber or mineral fiber such as glass wool and rock wool, etc.However, sound-absorbing material 51 can be made of synthetic resin foamsuch as polystyrene-based resin and polyethylene-based resin, etc., orflexible material such as urethane and rubber, or porous material.

The sound-absorbing unit 50 of this embodiment is placed on a supportbase 80 such as a body panel of a vehicle with its sound-absorbingmaterial 51 facing toward the space where there are sound waves to beabsorbed. With this placement, the first air layers 70 are definedbetween the sound-absorbing material 51 and the corrugated partitionplate 52, while the second air layers 75 are defined between the supportbase 80 and the corrugated partition plate 52. In other words, thecorrugated partition plate 52 is provided such that it divides the airlayer between the support base 80 and the sound-absorbing material 51into the first air layers 70 on the side of the sound-absorbing material51 and the second air layers 75 on the side of the support base 80. As aresult, the above-mentioned standing-waves are formed inside the firstand second air layers 70, 75, respectively, when the sound waves enterfrom both sides of the sound-absorbing unit 50.

Concerning the placement procedure of the sound-absorbing unit 50, it isnoted that you may attach the sound-absorbing material 51 to thecorrugated partition plate 52 by means of an adhesive or screws, etc.,and then place this combination on the support base 80. Alternatively,you may set the sound-absorbing material 51 so as to form the air layerbetween the sound-absorbing material 51 and the support base 80 and thenposition the corrugated partition plate 52 between them such that it candivide the air layer. The means for supporting the corrugated partitionplate 52 may be varied depending on the place where sound-absorbing unit50 is located. For example, you may simply place it on the support base80 or fix it to the support base 80 by an adhesive, clips, screws, etc.

The thickness D (depth) of the first air layer 70 is set to beone-fourth of the wavelength λ of the target sound waves that should beabsorbed according to the above-mentioned principle (see FIGS. 1A and1C). This enables the sound waves entering from the sound-absorbingmaterial's side to be absorbed efficiently, because the sound waves passthrough the sound-absorbing material 51 at maximum particle velocity.

It is noted that, in the case of the target frequency band being wide,the thickness D may be set differently for every first air layer 70,and/or it may be varied along the direction of the antinode portions 52a, 52 b. Such a change in the thickness D of the first air layers 70 maybe implemented by varying the amplitude of the corrugated partitionplate 52 or by forming projections and depressions on thesound-absorbing material 51. In the former case, the amplitude of thecorrugated partition plate 52 may be determined according to the contourof the surface of the support base 80, such as step height, in order tostabilize the sound-absorbing unit 50 in its place.

According to this embodiment, the sound-absorbing material 51 contactsthe corrugated partition plate 52 (i.e. upper antinode portions 52 a) byline contact. Therefore, the first air layers 70 are definedsubstantially by all the area behind the sound-absorbing material 51.This enables the sound-absorbing material 51 to exert the highsound-absorbing effect substantially all over its surface area. It isnoted that the neighboring first air layers 70 are not necessarilyisolated from each other, so some first air layers 70 may be incommunication with their neighboring first air layers 70. In otherwords, even if the sound-absorbing material 51 doesn't contact the upperantinode portions 52 a of the corrugated partition plate 52 and there isa certain clearance between them, the sound-absorbing material 51 canexert the high sound-absorbing effect substantially all over the surfacearea thereof.

By the way, in order to further improve the above-mentioned highsound-absorbing performance, it is important to promote the entry of thesound waves into the first air layers 70. For example, with suchlattice-type cells as shown in FIG. 1C, the sound waves cannot travelsmoothly inside the cell because the cross-sectional area (the area seenfrom above) of each cell is constant along the thickness direction.

To the contrary, according to this embodiment, the first air layers 70have a cross-sectional area that gradually increases from the bottomside (support base's side) to the opening side. This enables the gradualchange of the acoustic impedance, that is, a smooth sound wavepropagation inside the first air layers 70. With this arrangement, it ispossible to input the sound waves into the first air layers 70efficiently and thus to improve the sound-absorbing performance of thesound-absorbing unit.

Next, the sound-insulating performance of the sound-absorbing unit 50 ofthis embodiment is described in detail.

Generally, a sound-absorbing unit is placed in the space around thesound source such as an engine or in a cabin. Especially, in the case ofthe sound-absorbing unit being placed inside a space such as a cabin,theater room, etc., the most effective approach for improving thequietness of the space is to block the sound incoming from the outsideof the space. Thus, for example, the sound-absorbing unit in a cabin isrequired to deliver a high sound-insulating performance against theexternal noise that may enter the cabin as well as the highsound-absorbing performance against the target sound inside the cabin.That is, the sound-absorbing unit is required to have a highsound-insulating capability on the side opposed to a body panel (supportbase 80) and high sound-absorbing capability on its cabin side.

According to the sound-absorbing unit 50 of this embodiment, thecorrugated partition plate 52 can block the external noise incoming fromthe side opposed to the support base 80. That is, the external noiseincoming from behind of the sound-absorbing unit 50 lose a significantpart of their energy at the time of transmitting through the corrugatedpartition plate 52 before reaching the sound-absorbing material 51.Furthermore, the corrugated partition plate 52 has a high stiffness dueto its corrugated cross-section. This means that sound transmission lossis large and the intensity level of a sound will be reducedsignificantly at the time of the transmission through the corrugatedpartition plate 52. Thus, the sound-absorbing unit 50 of this embodimentcan implement a high sound-insulating performance for an external noise.

Next, the improved placement of the sound-absorbing unit 50 of thisembodiment, which enables further improvement in a sound-insulatingcapability, is described.

Referring to FIG. 4A, the sound-absorbing unit 50 is placed with itscorrugated partition plate 52 being separated from the support base 80.In this placed state of the sound-absorbing unit 50, the lower antinodeportions 52 b of the corrugated partition plate 52 are separated fromthe support base 80 by the gap Δ. This prevents the vibration of thesupport base 80 from being transmitted to the corrugated partition plate52 directly and reduces the amount of transmitted sound at thecorrugated partition plate 52. Therefore, the sound-absorbing unit 50 ofthis embodiment is suitable for being placed on the support base 80 thatis easy to vibrate, such as a body panel.

It is noted that the corrugated partition plate 52 may be supported in avibration-free manner by separate support members (not shown) with ahigh stiffness. In this case, an additional sound-absorbing material maybe attached to the corrugated partition plate 52 on its side opposed tothe support base 80 such that the additional sound-absorbing material isseparated from the support base 80. This enables the sound wavesincoming from behind (i.e. from the side opposed to the support base 80)to be absorbed effectively.

Alternatively, in anothre placed state of the sound-absorbing unit 50,the corrugated partition plate 52 may be supported locally by thesupport base 80, as shown in FIG. 4B. More specifically, parts of lowerantinode portions 52 b of the corrugated partition plate 52, or some ofthe lower antinode portions 52 b may be mounted on the support base 80.In this case, the contact portions of the support base 80 are preferablylow-vibration portions or vibration-free portions, such as portionsreinforced with ribs or stiffeners, portions corresponding to nodes ofpossible vibration modes of the support base 80, etc.

Alternatively, in yet another placed state of the sound-absorbing unit50, the corrugated partition plate 52 may be supported by the supportbase 80 via the elastic elements 90 made of a flexible material andhaving a low elasticity characteristic, as shown in FIG. 4C. Preferably,the elastic elements 90 are located locally according to the lowerantinode portions 52 b of the corrugated partition plate 52. That is,the elastic elements 90 are positioned so as to be associated with partsof a lower antinode portions 52 b of the corrugated partition plate 52,or some of the lower antinode portions 52 b. In this case, at the pointswhere the elastic elements 90 aren't provided, the lower antinodeportions 52 b are separated from the support base 80, as in the exampleshown in FIG. 4B. In this way the direct transmission of the vibrationat these points can be avoided.

According to the sound-absorbing unit discussed with reference to FIGS.4A-4C, it becomes possible to significantly reduce the amount of soundtransmitted at the contact portions between the corrugated partitionplate 52 and the support base 80 without placing a conventional acousticinsulating material with high-destiny/thickness/weight between them.This also leads to a weight reduction of the sound-absorbing unit.

To summarize, the sound-absorbing unit 50 of the first embodiment canefficiently absorb the target noise by its sound-absorbing structure andcan efficiently prevent the entry of noise into the space (e.g., acabin) and thus can reduce the noise to be absorbed by thesound-absorbing material 51.

It is noted that in the above-mentioned embodiment the corrugatedpartition plate 52 has a wave-shaped cross-section, however, the presentinvention is not limited to this cross-section. For example, in analternative embodiment shown in FIG. 5A, the corrugated partition plate52 has a rectangular wave-shaped cross-section. In this alternativeembodiment, the ratio of the sound-absorbing capability to thesound-insulating capability may be optimized using the widths of thefirst and second air layer 70, 75 as parameters such that thesecapabilities can adapt to the respective noise levels on both sides ofthe sound-absorbing unit. For example, in the case of placing a higherpriority on a sound-absorbing capability, the width of the first airlayer 70 may be set larger than that of the second air layer 75 toincrease the area of the first air layer 70 behind the sound-absorbingmaterial 51.

Further, in alternative embodiments shown in FIGS. 5B-5D, the corrugatedpartition plate 52 has triangular, exponential horn-shaped, anddimple-shaped (egg-shaped) cross-sections, respectively. In theseembodiments, the entry of the sound waves into the first air layers 70can be promoted effectively since the acoustic impedance changesgradually inside the first air layers 70, as in the aforementioned firstembodiment.

According to the second aspect of the present invention describedhereafter, a sound-absorbing unit is provided which can effectivelyabsorb the sound waves with a variety of incident angles, based on theabove-mentioned principle.

FIG. 6A is a cross-sectional view of a sound-absorbing unit according tothe second embodiment of the present invention. FIG. 6B is a perspectiveview of the partition plates of the sound-absorbing unit of thisembodiment. The sound-absorbing unit 60 consists of a sound-absorbingmaterial 51, a partition plate 52 and second partition plates 53. Thesound-absorbing material 51 and the partition plate 52 can be configuredas the aforementioned embodiments (including alternative embodiments).The like components indicated by like references are the same as theaforementioned ones, unless otherwise specified.

The second partition plates 53 are substantially rectangular flat plate.The second partition plates 53 may be made of an aluminum or steelplate, as is the partition plate 52. According to this embodiment, thesecond partition plates 53 are placed in the direction X that issubstantially perpendicular to the direction Y in which the antinodeportions 52 a, 52 b of the corrugated partition plate 52 extend, asshown in FIG. 6B. In other words, the first and second air layers 70, 75extending in the ‘wave-streak direction’ of the corrugated partitionplate 52 (the direction Y in FIG. 6B) are partitioned by the secondpartition plates 53 that cross the antinode portions 52 a, 52 b. It isnoted that two second partition plates 53 are shown in FIG. 6B, however,the present invention is not limited to this number. The number of thesecond partition plates 53 may be determined according to the overallsize of the sound-absorbing unit 60.

The first and second air layers 70, 75 partitioned by the secondpartition plates 53 have the width W2 in the wave-streak direction Ythat is determined based on the above-mentioned principle, whileconsidering the target frequency band and the characteristics of theambient sound field, etc. The width W2 of the first and second airlayers 70, 75 may be set differently between every first and second airlayer 70, 75. In this case, the second partition plates 53 may havesteps in the direction Y at the boundary between the first air layers 70and the second air layers 75. Alternatively, the second partition plates53 may be the sector-shaped plates matched with the cross-section of thecorrugated partition plate 52. In this case, sector-shaped plates may bearranged on the surface of the corrugated partition plate 52 in ashifted manner. Further, the two neighboring second partition plates 53don't necessarily extend in parallel with each other. So, the respectivesecond partition plates 53 may extend in different directions.

The sound-absorbing unit 60 of this embodiment may be mounted on thesupport base 80 via the elastic element 90, as shown in FIG. 6A. It isnoted that elastic element 90 can be a low-destiny sheet materialbecause the corrugated partition plate 52 is equipped with thesound-insulating capability for noise coming from behind (the directionZ in FIG. 6B) as mentioned above. Alternatively, the sound-absorbingunit 60 of this embodiment may be placed so as to offer increasedsound-insulating performance, as are the ones shown in FIGS. 4A-4C.

Alternatively, the sound-absorbing unit 60 may be placed with both itssides exposed to an open space so that it can absorb the noise comingfrom both its sides, as shown in FIG. 7. In this variant, theaforementioned partition plates 52, 53 are placed between the twosound-absorbing materials 51 a, 51 b. This enables the noise coming fromboth sides of the sound-absorbing unit 60 to be absorbed efficiently.

According to the sound-absorbing unit 60 of the second embodiment, thesecond partition plates 53 have a function of limiting the incidentangle of sound waves, as mentioned above with reference to FIG. 1C.Thus, the above-mentioned standing-waves are formed inside thesound-absorbing unit 60, even if the sound waves enter in a slantingdirection along the wave-streak direction Y. Therefore, according to thesecond embodiment, even if the sound-absorbing unit 60 is placed in asound field in which there are a variety of incident directions of soundwaves, the above-mentioned high sound absorbing effect is notdistributed over a wide frequency range other than the target frequencyrange.

Furthermore, in this second embodiment, the second partition plates 53enable in-plane rigidity (the rigidity against the load applied in thedirection Z) of the corrugated partition plate 52 to increase. That is,the second partition plates 53 also have a function of preventing thecorrugated partition plate 52 from deforming into a flattened structure.Thus, the sound-absorbing unit 60 is given sufficient strength that isrequired for an interior component. In addition, the sound-absorbingunit 60 can hold its function for a long time, without being deformed ordamaged, even if it is placed where it is likely to be subjected to theload from above, such as the floor of a cabin.

Next, several variants of the above-mentioned second embodiment aredescribed with reference to FIGS. 8A and 8B.

In FIG. 8A, the second partition plates 53 which partition only thefirst air layer 70 are shown as indicated by shading. According to thisvariant, additional weight reduction of the sound-absorbing unit 60 isachieved by partitioning only one of air layers (in this example, thefirst air layer 70 lying on the cabin's side). The sound-absorbing unit60 of this variant is suitable when it is required to offer the highsound-absorbing performance only on its one side.

It is noted that the second partition plates 53 may partition only apart of the air layer (in this example shown in FIG. 8A, only the upperpart of first air layer 70 is partitioned). Further, it is also possibleto tune the sound-absorbing/insulating capabilities by a combinationwith the second partition plates 53 as shown in FIG. 8B, consideringnoise levels on both sides of the sound-absorbing unit 60.

In the variant shown in FIG. 9A, the corrugated partition plates 52 havea wave-shaped cross-section whose phases and/or heights vary at theintersections of the corrugated partition plates 52 and one of thesecond partition plates 53. In other words, the second partition plates53 are placed between the corrugated partition plates 52 with differentphases and/or heights.

According to this variant, the sound-absorbing unit 60 can have a highsound-absorbing effect over a relatively wide frequency band by virtueof the difference in phases and/or heights of the corrugated partitionplates 52. In addition, an out-of-plane rigidity (the rigidity againstthe load applied in the direction Y) of the second partition plates 53can be increased by virtue of the difference in phases and/or heights ofthe corrugated partition plates 52. This increases durability of thesound-absorbing unit 60. Thus, the sound-absorbing unit 60 of thisvariant is suitable for being placed in a space where there are noiseover a relatively wide frequency band and loads applied from variousdirections, such as the floor of a cabin where the sound-absorbing unit60 is likely to be subjected to loads by legs of occupant.

FIG. 9B is a cross-sectional view of the sound-absorbing unit 60 in FIG.9A, as viewed along direction Y. In FIG. 9B, the corrugated partitionplate 52 (its cross-section drawing is indicated by a dotted line inFIG. 9B) has its phase shifted by π and is half height with respect tothose of its neighboring corrugated partition plate 52 (indicated by thesolid line). It can be easily understood from FIG. 9B that the strengthof the second partition plates 53 against the load in the direction Y isincreased and damage to the upper portions A of second partition plates53 can be avoided.

Similarly, the corrugated partition plate 52 (shown in FIG. 10A) mayhave a different pitch W1 with respect to that of its neighboringcorrugated partition plate 52 as shown in FIG. 10B. Further, the pitchW1 and/or depth may vary along the direction X, as shown in FIG. 10C.

According to the third aspect of the present invention describedhereafter, a sound-absorbing unit is provided which has a partitionplate that can simultaneously achieve functions of the corrugatedpartition plate 52 and the second partition plates 53.

FIG. 11A is a cross-sectional view of a sound-absorbing unit accordingto the third embodiment of the present invention. FIG. 11B is aperspective view of the partition plate of the sound-absorbing unit ofthis embodiment. The sound-absorbing unit 70 consists of asound-absorbing material 51 and a partition plate 54. Thesound-absorbing material 51 can be configured as in the aforementionedembodiments.

The sound-absorbing unit 70 of this embodiment may be configured andplaced as in the aforementioned embodiments (see FIGS. 4A-4C and FIG.7). For example, the sound-absorbing unit 70 may be mounted on thesupport base 80 via the elastic element 90, as shown in FIG. 11A. It isnoted that elastic element 90 can be a low-destiny sheet materialbecause the partition plate 54 is equipped with the sound-insulatingcapability for noise coming from behind, as the corrugated partitionplate 52 mentioned above.

According to this embodiment, the partition plate 54 is made of aluminumplate, etc. which has a plurality of recesses 54 d. The partition plate54 is provided with a sound-absorbing material 51, as in theaforementioned embodiments. The sound-absorbing material 51 and theouter surfaces of the recesses 54 d define the first air layer 70. Thethickness of the first air layer 70 is set to one-fourth of thewavelength λ of the target sound waves or the odd multiples ofone-fourth of the wavelength λ, as in the aforementioned embodiments.

As shown in FIG. 11A and FIG. 11B, the recesses 54 d have a circularcross-section (in the X-Y plane) whose radius decreases gradually towardthe support base 80. The recess 54 d is rotationally symmetric aroundthe pivot axis that passes through the center of the circularcross-section. However, the present invention is not limited to thisconfiguration. For example, the cross-section of the recess 54 d may beoval, trapezoid, etc. Further, the configuration of the recess 54 d maybe a polygonal pyramid such as triangular pyramid and rectangularpyramid, or a truncated polygonal pyramid, or a polygonal pyramid whosetop is rounded off. In FIG. 12A and FIG. 12B, truncated rectangularpyramid-shaped recesses 54 d are shown.

Preferably, the recesses 54 d are placed at high density so as toincrease the area of the air layer (i.e. the first air layer 70) behindthe sound-absorbing material 51 as much as possible. Further, theopening shape of the recess 54 d (i.e. pitches W1 and W2) may bedetermined based on the above-mentioned principle, while considering thetarget frequency band and the characteristics of the ambient soundfield, etc.

According to the sound-absorbing unit 70 of the third embodiment, thesound waves incident from various directions can be absorbed efficientlyand a sound absorbing effect is not distributed over a wide frequencyrange other than the target frequency range, as in the secondembodiment. In addition, the partition plate 54 with the recesses(cells) 54 d can be formed by stamping a sheet or integral foam-moldingof resin. This leads to a reduction in parts count for a sound-absorbingunit and eases assembly for a sound-absorbing unit. Furthermore, theentry of the sound waves into the recesses 54 d can be promotedeffectively because the cross-sectional area of the recess 54 d changesgradually along the direction Z and thus the acoustic impedance changesgradually inside the recesses 54 d. Further, the partition plate 54 hasa high rigidity against loads in every direction by virtue of the shapeof the recesses 54 d. This yields a high sound-insulating performancefor the sound waves incident from various directions as well as a highstrength for the loads applied from various directions. Thus, thesound-absorbing unit 70 of this embodiment is suitable for being placedin a space where there can be noise traveling in various directions andloads applied from various directions, such as the floor of a cabin.

The present invention is disclosed with reference to the preferredembodiment. However, it should be understood that the present inventionis not limited to the above-described embodiments, and variations andmodifications may be made without departing from the scope of thepresent invention.

For example, in the aforementioned third embodiment, some recesses 54 dmay have different shapes and/or depths with respect to other recesses54 d. Further, in FIG. 11B and FIG. 12B recesses 54 d formed regularlyare shown, however, the positions and shapes, etc. of the respectiverecesses 54 d may be optimized according to the sound fieldcharacteristics in the vicinity of the sound-absorbing unit.

Further, the sound-absorbing material 51 is placed on the opening sideof the recesses 54 d such that it covers the recesses 54 d in theaforementioned third embodiment. However, the sound-absorbing material51 may be placed on the opposite side such that it covers the bottomside of the recesses 54 d. In this case, the sound-absorbing material 51may replace the elastic elements 90 shown in FIG. 11A. With thisarrangement, the sound waves entering into the second air layer 75 canbe absorbed efficiently.

Further, the sound-absorbing unit in a cabin is described by way ofillustration in the above-described embodiments; however, thesound-absorbing unit may be placed in an engine room, for example.Further, the sound-absorbing unit according to the present invention mayact as an acoustic insulating unit used in a house (e.g., the spaceinside a double ceiling or floor), or a sound-proof wall disposed on aroadside. Further, the sound-absorbing unit according to the presentinvention is applicable to every portion of a cabin, such as a roof, afloor, a dash panel, a door, etc.

1. A sound-absorbing structure, comprising: a substantially flat supportbase; a substantially flat sound-absorbing material arrangedsubstantially parallel to the support base; and a corrugated partitionplate interposed between the support base and the sound-absorbingmaterial, the corrugated partition plate having upper antinode portionsopposed to the sound-absorbing material and lower antinode portionsopposed to the support base; wherein the lower antinode portions of thecorrugated partition plate are at least partially separated from thesupport base.
 2. The sound-absorbing structure as claimed in claim 1,wherein parts of the lower antinode portions of the corrugated partitionplate are supported via an elastic element by low-vibration portions ofthe support base.
 3. A sound-absorbing unit comprising: a corrugatedpartition plate having a first side and a second side opposite to thefirst side; a substantially flat sound-absorbing material provided onthe first side of the corrugated partition plate; and at least onesecond partition plate configured to partition air spaces definedbetween the sound-absorbing material and the corrugated partition plate.4. The sound-absorbing unit as claimed in claim 3, wherein the secondpartition plate extends in a direction substantially perpendicular to adirection in which antinode portions of the corrugated partition plateextend.
 5. The sound-absorbing unit as claimed in claim 3, furthercomprising a second sound-absorbing material provided on the second sideof the corrugated partition plate.
 6. The sound-absorbing unit asclaimed in claim 3, wherein the second partition plate is provided onlyon the first side of the corrugated partition plate.
 7. Thesound-absorbing unit as claimed in claim 3, wherein the corrugatedpartition plate includes a wave pattern whose phase is shifted at anintersection of the corrugated partition plate and the second partitionplate.
 8. The sound-absorbing unit as claimed in claim 3, wherein thecorrugated partition plate includes a wave pattern whose amplitude isvaried at an intersection of the corrugated partition plate and thesecond partition plate.
 9. The sound-absorbing unit as claimed in claim3, wherein the corrugated partition plate includes a sine wave pattern.10. The sound-absorbing unit as claimed in claim 3, wherein thecorrugated partition plate includes a rectangular wave pattern.
 11. Thesound-absorbing unit as claimed in claim 3, wherein the corrugatedpartition plate includes wave patterns with different frequencies. 12.The sound-absorbing unit as claimed in claim 3, wherein the corrugatedpartition plate includes wave patterns with different amplitudes.
 13. Asound-absorbing unit comprising: a partition plate having a plurality ofrecesses formed in a first side thereof, each of said recesses having anopening with a predetermined shape on the first side; and asound-absorbing material provided on the first side of the partitionplate to cover the openings of the recesses, wherein each of therecesses has a cross-sectional area that gradually varies with a depthof the recess.
 14. (canceled)
 15. The sound-absorbing unit as claimed inclaim 3, wherein the thickness of air spaces behind the sound-absorbingmaterial is set to odd multiples of one-fourth of the wavelength ofsound waves of target frequencies.